The present invention relates to endosteal implants, and more particularly to symphyseal-rami endosteal implants.
The conventional symphyseal-rami implant (commonly called a ramus frame implant) is a one-piece endosteal implant designed for use in the edentulous mandible. The implant is typically used where conventional endosteal or sub-periosteal implantation cannot be used because of inadequate bone, anatomical anomalies, or medical or economic considerations. The implant comprises a bar of biocompatible metal curved to follow generally the occlusal plane and having ends extending directly into each ramus and, depending from the center thereof, a symphysis portion. The tripodial design offers exceptional stability, the bar being supported by the symphysis anteriorly and the two ascending rami posteriorly. The frame or curved bar continuous with the endosteal portions lying above the gingiva supports the patient's mandibular prosthesis. The conventional implant and the technique for using the same is described in an article by Robert E. Nelson entitled "The Ramus Frame Implant for Stabilizing Impossible Mandibular Dentures" (Oral Implantology, Vol. IV, No. 4, Spring 1974, pages 475-503).
While the conventional one-piece implant has proven to be a valuable new technique for aiding "denture cripples" who could not otherwise be provided with dentures, it has not proven to be entirely satisfactory. Obviously it is desirable that the endosteal or bone-penetrating portions of the implant be disposed in the mandible in a totally passive manner, i.e., without exerting lateral or torque forces on the bone. This cannot be accomplished with the conventional one-piece frame which must be bent and sprung into place, thereby causing excessive pressure to the buccal plate of bone in the ramus areas. Indeed, the bending of the frame causes a considerable weakening of the metal as well as surface scratches thereon. Furthermore, to allow seating of the ramus implant, the bone grooves must be overextended, thus requiring a great deal of undue trauma to the bone during insertion. Finally, due to differences in the size and curvature of the symphysis area of bone, the symphysis portion must be adjusted by extensive bending and grinding procedures which necessitate resterilization of the implant before final seating thereof in the bone.
Even after the conventional implant is in place, additional problems present themselves. The soft tissue covering the ascending rami is only loosely attached to the bone, so that the tissue tends to move along the protruding portion of the bar during movement of the mandible. As the surgical metal of the implant is not fully compatible with the soft tissue, there results tissue irritation and tissue inflammation, as well as infiltration of bacteria and germs through the loose seal between the tissue and the metal. Furthermore, if any portion of the implant eventually fails and requires removal, it is necessary to remove the entire implant for repair or replacement.
One recent improvement to such implants involves the separation of the one-piece frame into three pieces: a symphysis blade and two ramus blades. The symphysis blade has a first portion adapted to be received in the symphysis bone, and each ramus blade has a first portion adapted to be received in an associated ramus bone. The symphysis blade has a second portion comprising a solid bar curved to meet the configuration of the symphysis bone and extending toward the ramus blades at each end, while each ramus blade has a second portion comprising a solid bar extending toward the symphysis blade. The ends of the second portions of the blades are adjusted by bending and shortening the opposing ends until they are in contact. The three pieces are then stabilized with overlaying clamps which lock the ends of the second portions together. This modification has not proven to be entirely satisfactory in use as the locking of the second portion ends by the clamp fails to provide sufficient strength to resist the tremendous pressures created by mastication. Furthermore, the three-piece implant, while more easily and more passively inserted than the one-piece implant, still requires considerable adjustments for proper fitting.
To remedy the strength deficiencies of the three-piece implant, it has been proposed to provide a male/female engagement between the ends of the second portions of the blades, each end of the symphysis blade second portion being hollowed to receive an associated projecting end of a ramus blade second portion. However, whereas the early clamping embodiment of the three-piece implant permits the blades to be inserted totally passively, the later male/female version does not, thus re-introducing the torquing problems associated with the conventional one-piece insert.
Accordingly, it is an object of the present invention to provide a symphyseal-rami endosteal implant in which the endosteal portions of the implant can be placed totally passively into bone.
Another object is to provide such an implant which is substantially compatible with the soft tissue covering the ascending rami to minimize tissue irritation and inflammation and provide a closer seal around the protruding implant to protect the bone from infiltration of bacteria and germs.
A further object is to provide such an implant in which a failed portion can be removed and replaced without disturbing the remainder of the implant.
It is also an object to provide such an implant which can be easily inserted in place without requiring any bending of the metal thereof.
It is another object to provide such an implant which is of sufficient structural to withstand the forces generated during mastication.